The present invention is directed to the total containment welding of plastic tubes. Various prior art exists disclosing different approaches to welding plastic tubes together and to the cutting of a plastic tube for separation into two tube segments. A general approach when welding two plastic tubes together is to clamp each tube in a tube holder with a portion of the tube extending outwardly of its holder. Each tube may be, for example, bent so that the bent ends of the two tubes are disposed toward each other. A heated wafer then passes through the bent ends of the two tubes to melt the bent ends and remove the bent portions. After the wafer is moved downstream away from the tubes, the tubes are pressed into contact with each other so that the melted tubes are welded together. This results in two main portions of the tubes being in communication with each other to form a unitary welded tube. In addition, the free ends or stubs of the bent tubes are also welded together and may be discarded or used for purposes of collecting samples, etc.
One known form of wafer is a metal plate which is folded upon itself to create a pair of sides. When the wafer is heated the lead end of the wafer begins to melt the plastic tubes as the wafer begins to pass through the spacing where the tubes extend from their holders. The melted plastic material is then deposited on the sides of the wafer. An advantageous form of this wafer is to include a scoop on each of the side walls so that the scoop collects the melted material at the bent ends when the wafer passes through the spacing between the holders.
An object of this invention is to provide a heatable wafer which includes structure for assuring an effective weld of the melted tube sections.
A further object of this invention is to provide such a wafer which increases the resulting weld strength of the welded tubes.
In accordance with this invention the wafer is in the form of a heatable plate having opposed side walls and a leading end and a trailing end. An outwardly extending scoop is formed on each of the side walls between and spaced from the leading end and the trailing end. Each scoop is open toward the leading end to remove a portion of the material of the plastic tubes as the heated wafer is moved between and in contact with the exposed portions of the tubes. In accordance with this invention a plurality of, and preferably two, slits are formed in the trailing end of the wafer in line with the scoops for minimizing the amount of plastic material that would remain on the wafer when the wafer is removed from the weld area.
The slits are of sufficient length to permit the melted plastic to be easily removed from the moving wafer and remain available as a weld pool when the melted ends of the tubes are pressed into contact with each other. A preferred length of the slits is 2 mm.
The invention may be practiced where the scoops have a leading surface that is tapered inwardly to facilitate the plastic material being collected into the scoops.